Ram Adhar Singh

Schottky diodes based on some semiconducting polymers

Recently there has been growing interest in the fabrication of devices using organic electrical conductors. In this paper, we report the fabrication of Schottky diodes based on metal-semiconducting organic polymer/Pt and metal-semiconducting organic polymer/carbon systems. The conducting polymer used was polytoluidine, and the metals were Al, Cu and Zn. The current-voltage (I-V) plots for these systems were non-linear and capacitance-voltage plots were linear in reverse bias indicating rectification behaviour.

Is a full team required for emergency management of pediatric trauma

Pediatric trauma centers often do not meet the guidelines requiring a trauma team as recommended by the American Academy of Pediatrics (AAP). We reviewed our experience with a team consisting of a pediatric emergency physician, resident, nurse, and respiratory therapist. The surgical and pediatric critical care residents and staff were available within 5 minutes. We conducted a retrospective chart review of 146 patients (aged 8.1 +/- 4.8 years) between 1987 and 1989, with Injury Severity Scores (ISS) greater than or equal to 16 or admitted to the pediatric critical care unit. The time of presentation, surgical services consulted, and the nature of the injury were obtained from chart review. The Pediatric Trauma Score (PTS), the Revised Trauma Score (RTS), the Injury Severity Score (ISS), Glasgow Coma Scale (GCS) score, and Pediatric Risk of Mortality (PRISM) were used to determine the severity of insult and physiologic derangement on admission. The Modified Injury Severity Score (MISS) was determined and the Delta score for Disability Assessment was assigned at discharge. The Delta score was also determined at 3-month intervals up to one year. The probability of survival (Ps) was calculated, using the ISS and RTS. The Z statistic for this group of patients was then determined, using the Major Trauma Outcome Study (MTOS) methodology. The percentages of patients who were normal, disabled, and dead were 61%, 31.5%, and 7.5%, respectively, at 6 months follow-up. Eleven deaths were expected based on PRISM and TRISS analysis. Our mortality and morbidity figures were comparable with those of centers with teams based on AAP guidelines.(ABSTRACT TRUNCATED AT 250 WORDS)

An investigation on single crystal growth, structural, thermal and optical properties of a series of organic D–π–A push–pull materials

We present the large single crystal growth of a series of donor–π–acceptor (D–π–A) push–pull chromophores; 4-N,N-dimethylamino-β-nitrostyrene (1), 2-(4-(dimethylamino)benzylidene)malononitrile (2), ethyl 2-cyano-3-(4-(dimethylamino)phenyl)acrylate (3) and methyl 2-cyano-3-(4-(dimethylamino)phenyl)acrylate (4). Single crystals with good optical transparency were grown from a mixed organic solvent (1 : 1 acetone–methanol) applying slow evaporation techniques, and crystal dimensions up to 17 × 4 × 1 mm3 has been successfully achieved in the case of chromophore 4. A single crystal X-ray diffraction study revealed that two (3 and 4) of them belong to the triclinic crystal system with space group P, while 1 and 2 crystallize in orthorhombic and monoclinic crystal systems with space groups Pbca and P21, respectively. The packing in all the chromophores (except 2) is stabilized by C–H⋯π interaction. Thermal analysis shows higher thermal stability for 2 (Td = 354 °C), 3 (Td = 365 °C) and 4 (Td = 330 °C) than 1 (Td = 240 °C). The thermodynamic and kinetic parameters, such as heat and entropy of fusion, and activation energy have been determined by exploiting DSC and TGA data, respectively. A Lippert–Mataga plot reflects the highest change in dipole moment on excitation from ground state to excited state for chromophore 3 (4.80 D) followed by 4 (4.45 D), 2 (3.59 D) and 1 (3.17 D). We also report the quantum yield of all the chromophores in different organic solvents. In acetonitrile, it is 0.007, 0.014, 0.023 and 0.019 for chromophores 1, 2, 3 and 4; respectively. These studies indicate the potential opto-electronic application of these push–pull chromophores.

Pediatric trauma in southwestern Ontario: linking data with injury prevention initiatives

BACKGROUND Our objective was to provide an epidemiologic description of pediatric trauma in SW Ontario using multiple data sets. Injury prevention (IP) initiatives were linked with predominant injury mechanisms to determine whether IP programs were supported by data. METHODS Descriptive analysis was undertaken for five pediatric age groups (<1 year, 1-4 years, 5-9 years, 10-14 years, 15-19 years) using the Ontario Trauma Registrys Death Data Set, Comprehensive Data Set (Lead Trauma Hospitals [LTH] patients), and Minimal Data Set (hospital admissions), 1999-2000, for all pediatric patients residing in SW Ontario. National Ambulatory Care Reporting System (NACRS) data from the Childrens Hospital of Western Ontario/London Health Sciences Centre were used to capture the Emergency Room (ER) injury data. Information on IP initiatives for children and youth was gathered through an Internet search, supplemented by a survey. RESULTS Injury in SW Ontario resulted in 13,197 ER visits, 1,616 hospital admissions, 70 severe trauma (ISS > 12) cases treated at a LTH and 47 deaths to children and youth. More males than females were injured, with the sex differential more pronounced as age increased. Falls were the leading mechanism for ER visits (37%) and hospital admissions (26%). Recreational injuries represented approximately 30% of injuries to the 10-14 yr age group. As ISS increased, MVCs emerged as an important mechanism, representing 71% of LTH cases and 53% of pediatric injury deaths in SW Ontario. There were 61 pediatric IP programs identified in SW Ontario. Eighty-four percent of programs (51/61) were supported by data, and were related to one of the predominant injury mechanisms. CONCLUSIONS Injury is a serious problem for children in SW Ontario. Data can be used to identify modifiable risk factors to develop and implement new IP initiatives with the goal of reducing childhood injury and death. There is a need to integrate and link IP programs in SW Ontario for full coverage of all injury mechanisms.

Preparation and characterization of polymer composites based on charge-transfer complex of phenothiazine-iodine in polystyrene

Polymer composites based on charge-transfer complex of phenothiazine and iodine with polystyrene have been prepared in different weight ratios and characterized by FTIR, XRD, mechanical, microstructure and electrical properties (d.c. as well as a.c.). These composites show semiconducting behaviour as the conductivity increases with increasing temperature. Low percolation threshold (10% wt CTC) has been found indicating that processable conducting polymers with improved mechanical properties can be prepared by this method.

Molecular semiconductors based on charge transfer complexes of some substituted phenothiazines with tetracyanoethylene

Abstract Molecular semiconductors based on charge transfer complexes of tetracyanoethylene (TCNE) with phenothiazines namely phenothiazine, 2-chlorophenothiazine, 2-acetylphenothiazine and 2-(trifluoro)methylphenothiazine have been prepared and characterized by elemental analysis, thermal, spectral and X-ray diffraction methods. The thermal decomposition behavior of these materials indicates that they are thermally stable up to about 100°C and then proceed to stoichiometric (1:1) weight losses corresponding to TCNE and phenothiazines. The stoichiometries were confirmed further from the combustion data. The existence of radical cations of phenothiazines and radical anions of TCNE were confirmed from their electronic and infrared spectral data. The preferential complexation with H-intra form of phenothiazines were indicated by their 1H NMR spectra. These materials were polycrystalline in nature and the powder X-ray diffraction data give their structures to be orthorhombic. The electrical conductivities are ...

Molecularly dispersed polymer composites of charge-transfer materials: morphology and physical properties

Abstract The dispersed type of composites of two conducting charge-transfer materials {phenothiazine–iodine (in 2:3 molar ratio) and benzidine–iodine (in 1:1 molar ratio)} in insulating polymer, polystyrene have been prepared and characterized by FT-IR, XRD and for their microstructure, electrical properties (d.c. as well a.c.) and mechanical properties. A correlation between the morphology and physical properties has been made on the basis of data obtained. The method leads to an alternative route for the preparation of processable conducting polymers with improved mechanical properties in which the conductivities could be controlled by the loading of insulating polymers with conducting charge-transfer materials.

MICROSTRUCTURAL AND THERMAL STUDIES ON CHARGE-TRANSFER MATERIALS

Abstract Microstructural and thermal studies on charge-transfer materials have been reported in this paper. Optical microphotographs of pure donors, acceptors and their compiexes have been obtained. Thermal analysis has been done to learn about their thermal stability and stoichiometries. Th solidification kinetics has been studied to learn about the role of heat treatment on these materials. Powder X-ray diffraction data and optical microphotographs have been obtained to evolve structure-microstructure - physical property correlations. It has been shown that these aspects, hitherto neglected, should be seriously pursued for developing a commercially viable process for organic electronic materials.

Possibility of fractal growth in polymer composites of charge-transfer materials

Abstract The possibility of fractal growth in polymer composites of charge-transfer materials by analysing the optical image has been reported. Charge-transfer complexes usually grow in reticulate (net-like) or in a channel form in nonconducting polymers. We report, for the first time, an unusual growth in polymer composite of charge-transfer materials (phenothiazine—TCNQ) in poly(vinyl acetate). The surface coverage is found to be about 70%. The double logarithmic plot of N(R) , number of boxes needed to cover the object completely, and R , reduction factor of each box to the initial object, has been plotted and the fractal dimensions have been found to be 1.8 and 1.4 in two different regions.

Mixed conduction in charge transfer materials based on aromatic diamines and iodine having different mole ratios

Mixed ionic and electronic conduction in charge transfer materials based on aromatic diamine electron donors (benzidine,o-tolidine (3,3′-dimethyl benzidine) andN,N′-diphenylbenzidine) with iodine in different mole ratios has been reported. The current-voltage and capacitance-voltage curves as a function of time and temperature have been obtained to determine the role of ionic conduction in electronic conductors based on charge transfer complexes. The compositional dependence of ionic transport numbers, diffusion parameters, ionic(σi) and electronic(σe) conductivities and thermal activation energies has been studied. Temperature and frequency dependence of AC impedance and related parameters have been studied to learn about the electrical conduction behaviour in these non-stoichiometric charge transfer materials. An electrochemical mechanism has been proposed to account for the ionic conduction in some of these complexes.